1. Field of the Invention
This invention relates generally to cooling of vanes in a combustion gas turbine and, more particularly, to a flow control insert which can be placed in a cooling passage of a turbine vane to simultaneously reduce cooling air flow and increase heat transfer from the vane to the cooling air, thereby improving efficiency of the turbine via reduced cooling air flow requirement while maintaining vane temperature within a specified range.
2. Description of the Related Art
Combustion gas turbines are clean-burning, efficient devices for generating power for a variety of applications. One common application of combustion gas turbines is in power plants, where the turbine drives a generator which produces electricity. Such stationary gas turbines have been developed over the years to improve reliability and efficiency, but the continuous improvement quest never ends.
Turbines operate at very high temperatures and pressures, and cooling of internal components is required in order to prevent damage. However, pumping of large volumes of cooling air consumes a significant amount of energy, thus representing a parasitic loss of efficiency for the whole engine. It is therefore desirable to reduce the cooling air flow requirement of a turbine, although component temperatures must be maintained within an acceptable range as determined by material thermal limits and desired component life.
Turbine vanes are stationary airfoils which are arranged in circumferential rows inside the turbine, where rows of vanes are alternately positioned between rows of turbine blades. Because the vanes are directly exposed to the combustion gas, they get extremely hot and are therefore designed with internal cooling air passages to maintain temperature within specification. In addition, turbine vanes are often coated with a thermal barrier coating, such as a ceramic material with extremely high temperature capability.
The design and tooling of a turbine and all of its components is very expensive. Therefore, fully validated and time-tested components such as vanes are not frequently re-designed. However, even with existing vane designs, it is possible and desirable to improve turbine efficiency via reducing cooling air flow requirements, where the reduced volume of cooling air flow still maintains the vane within a specified temperature range.